1. Field of the Invention
The present invention generally relates to radio equipment for transmitting a digital signal and its peripheral apparatus, and more particularly, to radio equipment and its peripheral apparatus for suppressing interference to a radio signal which is generated by the digital signal.
2. Description of the Related Art
Recently, a variety of radio communication systems such as a portable telephone service system are developing and a wide range of radio frequencies are used for the systems. For such a system using a wide range of radio frequencies, a digital modulation method capable of achieving higher usage efficiency of the frequencies is being used instead of an analog modulation method. For example, portable telephone service systems operating at the 800-MHz band and 1.5-GHz band are already in commercial use by the digital modulation method of xcfx80/4-shifted quadrature phase shift keying (QPSK).
Further, transmission rate and processing speed of the digital signal also increase according to development of LSI technologies. Therefore, frequencies of a timing clock of the digital signal and a clock for processing the digital signal increases close to a carrier frequency for radio transmission.
Since the digital signal and the clock signal are formed by rectangular waves, these signals have a number of high-order harmonic components. Frequencies of the harmonic components are spread to UHF and VHF bands. Therefore, when the frequencies of the harmonic components are present in a receiving frequency band of a radio signal, the harmonic components enter a receiving circuit of radio equipment as interference and have influence on a desired signal. The harmonic components are obtained by Fourier-expanding a digital signal k(t) as follows:       k    ⁢          (      t      )        =            A      /      2        ⁢          {              1        +                  "AutoLeftMatch"                                    (                              4                /                π                            )                        ⁡                          [                                                cos                  ⁢                                      xe2x80x83                                    ⁢                                      ω                    o                                    ⁢                  t                                -                                                      (                                          1                      /                      3                                        )                                    ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                  3                  ⁢                                      ω                    o                                    ⁢                  t                                +                                                      (                                          1                      /                      5                                        )                                    ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                  5                  ⁢                                      ω                    o                                    ⁢                  t                                -                                                      (                                          1                      /                      7                                        )                                    ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                  7                  ⁢                                      ω                    o                                    ⁢                  t                  ⁢                                      xe2x80x83                                    ⁢                  …                                            ]                                }                    
According to the above equation, the harmonic components have odd-order frequency components.
In general, to miniaturize size of the radio equipment, radio parts and digital signal processing parts are arranged close to each other in the same housing. To improve transmission quality and to reduce power consumption, a highly-sensitive receiver has also been developed. Therefore, in such a configuration, the above-mentioned interference due to harmonics may cause a larger problem.
In Japanese Laid-Open Patent Applications No.3-255510 and No.5-90987, methods of frequency-modulating a clock signal of a clock oscillator for a control circuit such as a CPU are disclosed. By the frequency modulation, the spectrum of harmonics of the clock signal is spread, and levels of high-order harmonics may be reduced. Therefore, interference to a receiving circuit may also be reduced. More specifically, Japanese Laid-Open Patent Application No.5-90987 shows an embodiment in which the above-mentioned method is applied to radio equipment using an analog modulation and demodulation method.
However, in radio equipment using a digital modulation and demodulation method, a digital signal such as transmission data as well as the clock oscillator of the control circuit also generates high-order harmonics. When increasing frequency deviation of the modulation of the clock signal in the control circuit to further reduce the level of the harmonics of the clock signal, an error may occur in an operation of the control circuit. Furthermore, the clock frequency is increasing, and the high-order harmonics may easily have influence on the radio signal.
FIG. 1 shows a block diagram of typical digital radio equipment. The equipment 1 shown in FIG. 1 includes a transmission part and a reception part. The transmission part comprises a data processing circuit 2, a modulator 4, and a transmitting circuit 6. The reception part comprises a receiving circuit 8, a demodulator 10, and a data processing circuit 12. The data processing circuit 2 includes a speech CODEC 16 and a signal processing circuit 18. The data processing circuit 12 includes a signal processing circuit 20 and a speech CODEC 22.
In the speech CODEC 16, a speech signal is converted to digital data based on a timing clock from a clock oscillator 30. In the signal processing circuit 18, the digital data is formatted in a format suitable for being transmitted. For example, when the radio equipment 1 operates in a time division multiple (TDM) system, the digital data is distributed to TDM frames. When the modulation method is QPSK, the digital data is separated to an I (in-phase) channel signal and a Q (quadrature phase) channel signal.
In the modulator 4, the digital data processed in the signal processing circuit 18 is filtered, and a first local signal is digitally modulated by the filtered digital data. For the digital modulation, phase modulation such as QPSK and frequency modulation such as GMSK are usable. An output signal of the modulator 4 is converted to a radio signal by the transmitting circuit 6, and is transmitted through a filter 40 to an antenna 42.
A radio signal which has come through the antenna 42 and the filter 40 is received in the receiving circuit 8, and is converted to an intermediate frequency signal. The intermediate frequency signal is demodulated in the demodulator 10 to reproduce digital data at a baseband frequency. The reproduced digital data is processed to digital data including a timing clock for the speech CODEC 22 in the signal processing circuit 20, and is converted to a speech signal in the speech CODEC 22.
The speech CODECs 16, 22 and the signal processing circuits 18, 20 may be commonly constructed with a digital signal processor (DSP). Timing clocks from the clock oscillator 30 are provided to the speech CODECs 16, 22, and DSP clocks from the clock oscillator 32 are provided to the signal processing circuits 18, 20. The speech CODECs 16, 22 and the signal processing circuits 18, 20 are connected to CPU 14 operable with a CPU clock provided from a clock oscillator 34 through a bus line.
In such a circuit configuration, the digital data is generated based on the timing clock for the speech CODEC and is formed by the rectangular waves. Therefore, the digital data includes a number of high-order harmonic components. When a frequency of one of the high-order harmonic components is close to the radio channel frequency, the harmonic component shown in a dotted line (A) may cause interference during operation of the receiving circuit 8.
The clock oscillators 30, 32 which generate the timing clock and the DSP clock for generating and processing the digital data have respectively high-frequency clock sources. Therefore, the high-frequency clock sources also generate high-order harmonic components which influence the receiving circuit 8. The interference is shown in dotted lines (B) and (C).
Further, the demodulator 10 commonly has a clock recovery circuit for recovering a timing clock to reproduce the baseband signal. Therefore, the clock recovery circuit and the reproduced baseband signal also generate high-order harmonic components which influence the receiving circuit 8. The interference is shown in a dotted line (D).
The CPU clock operating the CPU 14 and input and output data flowing through the bus line also generate high-order harmonic components which may cause interference. The interference is shown in dotted lines (E) and (F).
Still further, peripheral apparatuses such as a personal computer, a facsimile, a television, a radio, and a global positioning system (GPS), which are located close to the digital radio equipment 1, also have many clock oscillators. Therefore, harmonics are generated from those clock oscillators and harmonics are also generated from digital signals transmitting through cables which connect the peripheral apparatuses. These harmonics also influence the receiving circuit 8 of the digital radio equipment 1 as interference is shown in dotted lines (G) and (H).
Next, a detail description will be given of the interference by the timing clock generated in clock oscillator 30.
For example, when a bit rate of the timing clock is 11.2 kbps, the clock oscillator 30 has a 2.688-MHz clock source, and a signal divided by 24 is used as the timing clock. In this case, a 163-order harmonic of an output of the 2.688-MHz clock source is a 438.144-MHz signal. If a radio channel is used at a frequency of 438.150 MHz, the harmonic frequency is close to the radio channel frequency. The harmonic may interfere with the radio channel being received.
FIG. 2A and FIG. 2B show signal space diagrams when a QPSK signal is received with interference. FIG. 2A shows the signal space diagram at an instant of time, and FIG. 2B shows the signal space diagram averaged over a given time period. When the high-order harmonic component of the clock is added to an ideal QPSK signal, as shown in FIG. 2A, four ideal signal points of the QPSK signal are shifted by interference in the same direction. However, the shifted direction rotates about each signal point according to a frequency difference between the radio channel and the interference (in the previous example, 6 kHz). As a result, as shown in FIG. 2B, in averaging over the given time period, the four ideal signal points respectively spread in a circle form. The interference becomes a bright-line interference. When a size of the circle exceeds a decision level, an error occurs.
As mentioned above, in conventional digital radio equipment, since the data is formed by the digitally-shaped clock, the harmonics are generated from the digital data and the clock. Namely, the interference which did not occur in analog radio equipment is newly generated for the receiving circuit in digital radio equipment.
Further, for improving frequency utility and services, the data transmission speed needs to be increased. For this requirement, the clock sources of the clock oscillator for generating the timing clock and the DSP oscillator for processing the digital data tends to have a higher frequency. On the other hand, in a relatively low radio frequency, the digital modulation and demodulation methods are being used. Therefore, a level of interference due to the harmonics of the clock used for the digital data increases, and the interference may strongly influence the radio receiving circuit.
It is an object of the present invention to provide radio equipment and its peripheral apparatus in which harmonics generated by a digital signal are reduced and interference with a radio receiving circuit are also reduced. This permits the disadvantages described above to be eliminated.
The object described above is achieved by radio equipment for communicating digital data comprising: a clock modulation part for angular-modulation of a clock signal by a given modulation signal; and a data processing part processing the digital data based on the clock signal angular-modulated in the clock modulation part and producing angular-modulated digital data; wherein levels of harmonics generated from the clock signal and the digital data are reducible.
According to the above-mentioned radio equipment, the clock processing the digital data is angular-modulated and the spectrum of harmonics of the clock is spread. Therefore, the level of the harmonics is reduced and the interference due to the harmonics is prevented from influencing a radio receiving circuit in the radio equipment and external radio equipment.
The object described above is also achieved by radio equipment for communicating digital data comprising: a reception part for receiving a radio signal; a demodulation part demodulating the radio signal from the reception part and producing digital data; a clock recovery part for recovering a recovered clock in relation to the digital data from the demodulation part; and a recovered-clock modulation part angular-modulation of the recovered clock from the clock recovery part by a given modulation signal; wherein levels of harmonics generated from the recovered clock signal and the clock recovery part are reducible.
According to the above-mentioned radio equipment, the recovered clock is angular-modulated and the spectrum of harmonics of the recovered clock is spread. Therefore, the level of the harmonics is reduced and the interference due to the harmonics of the recovered clock is prevented from having an influence on a radio receiving circuit in the radio equipment and external radio equipment.
The object described above is also achieved by a clock modulation module comprising: a clock modulation part for angular-modulation of a clock signal by a given modulation signal; and a data processing part processing digital data for radio communication based on the clock signal angular-modulated in the clock modulation part, and producing angular-modulated digital data; wherein levels of harmonics generated from the clock signal and the digital data are reducible.
According to the above-mentioned clock modulation module, the clock for processing the digital data is angular-modulated and the spectrum of harmonics of the clock is spread. Therefore, the level of the harmonics is reduced and the interference due to the harmonics of the clock is prevented from having an influence on an apparatus located close to the clock modulation module.
The object described above is also achieved by radio equipment for receiving a radio signal modulated by angular-modulated digital data, the radio equipment comprising: a reception part receiving the radio signal; a demodulation part demodulating the radio signal in synchronization with frequency and phase variation of the angular-modulated digital data so as to produce digital data in which an angular modulation component is avoided.
According to the above-mentioned radio equipment, the angular-modulated digital data is demodulated in synchronization with frequency and phase variation of the angular-modulated digital data. Therefore, the angular-modulated digital data is properly demodulated without being influenced by the angular modulation.
The object described above is also achieved by the radio equipment mentioned above, wherein the radio equipment further comprises an interference detection part detecting interference to a received signal, and operation of the clock modulation part is based on an output of the interference detection part.
According to the above-mentioned radio equipment, when no interference is detected, the clock is not modulated. Therefore, at this time, the modulation of the clock is prevented from having an influence on other circuits.
The object described above is also achieved by the radio equipment mentioned above, wherein the radio equipment further comprises an interference channel table which stored receiving channels which are subjected to interference by harmonics generated in the radio equipment, and the clock modulation part operates when one of the receiving channels stored in the interference channel table is used.
According to the above-mentioned radio equipment, when a signal is received on the receiving channel which is not subjected to interference created by the harmonics of the clock, the clock is not modulated. Therefore, at this time, the modulation of the clock is prevented from having an influence on other circuits.
The object described above is also achieved by the radio equipment mentioned above, wherein the clock modulation part operates only during reception of a radio signal.
According to the above-mentioned radio equipment, when no signal is received, the clock is not modulated. Therefore, at this time, the modulation of the clock is prevented from having an influence on other circuits.
The object described above is also achieved by the radio equipment mentioned above, wherein the radio equipment further comprises a signal processing part which communicates the digital data by use of a time division multiple, a time interval of a time division frame given by integral multiples of a period of the given modulation signal for angular-modulation of the clock signal in the clock modulation part.
According to the above-mentioned radio equipment, the time interval of the time division frame is given by integral multiples of the period of the given modulation signal. No portion of the digital data in the frame is out of the frame and the amount of the transmission data in one frame is maintained. Therefore, influence due to the modulation of the digital data may be reduced.
The object described above is also achieved by an apparatus comprising: a control circuit processing data based on a clock signal; a transmission line transmitting angular-modulated data; and a modulation-component avoiding part, connected to the transmission line, to avoid a modulation component from the angular-modulated data from the control circuit so as to produce data in which the modulation component is avoided; wherein levels of harmonics generated from the angular-modulated data from the transmission line is reducible.
According to the above-mentioned apparatus, the data from the control circuit is angular-modulated by the given modulation signal, and the data is provided to other circuits after the modulation component in the data is avoided. Therefore, the level of the harmonics of the clock signal passing through the transmission line may be reduced, and the modulation of the data is prevented from having an influence on other circuits. More specifically, when the apparatus includes the radio equipment, the harmonic generated from the transmission line is prevented from influencing the receiving circuit.
The object described above is also achieved by an apparatus comprising a modulation-component avoiding part avoiding a modulation component from angular-modulated data transmitted from a first apparatus through a transmission line, and producing data in which the modulation component is avoided.
According to the above-mentioned apparatus, after the modulation component in the angular-modulated data coming from the first apparatus through the transmission line is avoided, the data is provided to other circuits. Therefore, the level of the harmonics of the angular-modulated data may be reduced, and the modulation of the data is prevented from having an influence on other circuit processing.
The object described above is also achieved by radio equipment for communicating digital data comprising: a clock oscillator generating a clock signal; and a carrier generation part generating a carrier based on a reference signal; wherein frequency of the reference signal is given by integral multiples of frequency of the clock signal.
According to the above-mentioned radio equipment, when the frequency of the reference signal is given by integral multiples of the frequency of the clock signal, frequency of higher-order harmonic of the clock signal may be identical to one of the carriers. In this case, interference due to the harmonic may be removed by demodulation using an offset control.
The object described above is also achieved by an apparatus positioned adjacent to radio equipment, comprising: a reference signal receiving part receiving a reference from the radio equipment for generating a carrier; and a control circuit operating based on the reference signal.
The object described above is also achieved by radio equipment positioned adjacent to a peripheral apparatus, comprising: a clock signal receiving part receiving a clock signal from the peripheral apparatus; and a carrier generation circuit generating a carrier based on the clock signal received from the peripheral apparatus through the clock signal receiving part.
According to the above-mentioned apparatus, the reference signal in the radio equipment is used as a clock of the control circuit. According to the above-mentioned radio equipment, the clock signal in the peripheral apparatus is used as the reference signal for generating the carrier. Therefore, the frequency of the harmonic generated from the control circuit in the apparatus may be identical to the frequency of the receive carrier of the radio equipment. In this case, interference to the receiving circuit due to the harmonic may be removed by demodulation using the offset control.
The object described above is also achieved by radio equipment comprising a reference signal connection part connecting, to a peripheral apparatus, at least one of a reference signal for generating a carrier and signals given by dividing the reference signal.
According to the above-mentioned radio equipment, the reference signal of the radio equipment may be easily provided to the peripheral apparatus.
The object described above is also achieved by radio equipment for receiving a signal modulated by digital data comprising: a reception part receiving the signal; a demodulation part demodulating the signal to produce digital data, the demodulation part comprising a carrier recovery part recovering a carrier from the signal; and a clock oscillator generating a clock signal; wherein frequency of a recovered carrier from the demodulation part is given by integral multiples of frequency of the clock signal.
According to the above-mentioned radio equipment, the frequency of the higher-order harmonic of the clock signal may be identical to one of the carrier frequencies. Therefore, the higher-order harmonic of the clock signal may have the same phase as that of the reference signal for detection. In this case, interference due to the harmonic may be removed by demodulation using the offset control.
The object described above is also achieved by an apparatus positioned adjacent to radio equipment, comprising: a recovered-carrier receiving part receiving a recovered carrier recovered from a received signal in the radio equipment; and a control circuit operating based on the recovered carrier.
According to the above-mentioned apparatus, the recovered carrier in the radio equipment is used as a clock of the control circuit in the apparatus. Therefore, the frequency of the harmonic generated from the control circuit in the apparatus may be identical to one of the carrier frequencies in the radio equipment. Therefore, the higher-order harmonic of the clock signal may have the same phase as that of the reference signal for detection. In this case, interference to the receiving circuit in the radio equipment due to the harmonic may be removed by demodulation using the offset control.
The object described above is also achieved by radio equipment comprising a recovered-carrier connection part connecting a peripheral apparatus to a recovered carrier recovered from a received signal.
According to the above-mentioned radio equipment, the recovered carrier in the radio equipment may easily be provided to the peripheral apparatus.
The object described above is also achieved by radio equipment for communicating digital data comprising: a clock oscillator generating a clock signal; an interference detection part detecting interference with a received signal; and a clock control part changing frequency of the clock signal so that the interference detected in the interference detection part decreases.
According to the above-mentioned radio equipment, as a result of changing the clock signal frequency, frequency of the harmonic of the clock signal may be identical to the received signal frequency. In this case, interference with the receiving circuit in the radio equipment due to the harmonic may be removed by demodulation using the offset control.
The object described above is also achieved by radio equipment for communicating digital data comprising: a timing clock oscillator generating a timing clock signal; a digital data generation part generating the digital data based on the timing clock signal; a transmission part transmitting a carrier modulated by the digital data; a reception part receiving a signal on a receiving channel; and an interference channel table storing receiving channels which are subjected to interference by harmonics of the timing clock signal and the digital data; wherein frequency of the timing clock signal is changed when one of the receiving channels stored in the interference channel table is used.
According to the above-mentioned radio equipment, the frequency of the timing clock signal is changed when one of the receiving channels stored in the interference channel table is used. Therefore, the harmonic of the timing clock signal is prevented from interfering with the receiving channel.
The object described above is also achieved by radio equipment having a reception part and a control part, the radio equipment comprising: a clock oscillator generating a clock signal in the control part; a phase shift part shifting the clock signal by 180 degrees; an adjustment part adjusting a level ratio of a 180-degree shifted clock signal to the clock signal; and an interference detection part detecting interference to a received signal in the reception part; wherein the level ratio is adjusted in the adjustment part so that a harmonic of the clock signal and a harmonic of the 180-degree shifted clock signal cancel each other and the interference is reduced.
According to the above-mentioned radio equipment, interference to the received signal due to the harmonic of the clock signal may be reduced.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.